With the increasing progress of CCD and DSP technology, low illuminance infrared video camera It is becoming more mature and stable, and many manufacturers (businesses) will video camera The illuminance parameters of 110 become lower as the scale increases, ranging from 1.0lux to 0.1lux, to 0.001lux, etc., but the camera may not have such high sensitivity. In order to truly understand the low illuminance infrared camera, we will analyze it from the following four aspects:
1、 Lens
As an important part of the infrared camera component, its role is to focus the light of the subject for the CCD of the infrared camera, so that the scene can be imaged on the CCD. The sharpness of CCD imaging is directly determined by the amount of light it can absorb. It is used to measure the amount of light taken by the lens, which is called the light entering amount. The light entering amount of the lens is expressed by the F value (aperture). F value=f (focal distance)/D (effective aperture of lens), which is inversely proportional to aperture and directly proportional to focal distance. Under the condition of the same focal length, the larger the lens aperture, the smaller the F value, and the larger the lens light input. Most of the F values of common lenses are 1.2 and 1.4. At present, there are also F1.0 lenses. Therefore, in order to make the infrared camera obtain the ideal low illumination effect, it is necessary to configure a suitable lens or a lens with a smaller F value.
2、 CCD photosensitive device
At present, there are three major suppliers of CCD commonly used for infrared cameras, namely SONY, SHARP and LG. Among these three kinds of CCD, SONY's CCD sensitivity is relatively good, and the commonly used SONY CCD low illumination technology is SuperHADCCD; Later, SONY developed a super sensitive CCD, which SONY called EXVIEWCCD. The sensitivity of this CCD is 5 times that of SuperHADCCD.
In addition, the size of CCD also has a great impact on the sensitivity. The larger the size, the better the sensitivity. In order to make the infrared camera have a lower illuminance index, a 1/2-inch CCD camera is often used. Data shows that the light sensitivity of 1/3-inch CCD is only 56% of that of 1/2-inch CCD; The sensitivity of 1/4-inch CCD is only 44% of that of 1/3-inch CCD.
3、 Image DSP processing
Since the development of low illumination infrared camera, not only the development of hardware technology, but also the outstanding performance of DSP image processing, such as color to black technology and low-speed electronic shutter, namely the emergence of frame accumulation technology.
4、 Color to black technology
Generally, the sensitivity of black and white cameras is much higher than that of color cameras. Because in black and white cameras, DSP operations only process two colors, namely black and white, so now quite a number of low illumination infrared cameras have the function of color to black and white, that is, the image is color in the daytime, and the image is converted into black and white by software processing at night, Lower illumination is achieved by sacrificing color effects.
Generally, the process of color to black and white is controlled by the intensity of the charge converted after the CCD collects the light. When the charge intensity reaches a certain critical value, it will automatically be converted into black and white images. Similarly, to ensure that there is no repeated switching at the critical value, a delay processing will be performed.
According to the above analysis, when selecting a low illumination infrared camera, users should not blindly look at the minimum illumination parameters marked by each business, but should select the corresponding low illumination infrared camera according to the application environment, requirements, monitoring objects, and economic ability.
